HR: 1340h
AN: B43D-0305    [Abstracts]
TI: Short-term Response of Soil Respiration to Simulated Rainfall in a Subtropical Savanna
AU: * Boutton, T W
EM: boutton@neo.tamu.edu
AF: Texas A&M University, Department of Rangeland Ecology and Management, College Station, TX 77843-2126 United States
AU: Bai, E
EM: ebai@tamu.edu
AF: Texas A&M University, Department of Rangeland Ecology and Management, College Station, TX 77843-2126 United States
AU: Hollister, E B
EM: ehollister@neo.tamu.edu
AF: Texas A&M University, Department of Rangeland Ecology and Management, College Station, TX 77843-2126 United States
AU: Midwood, A J
EM: a.midwood@macaulay.ac.uk
AF: Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, AB15 8QH United Kingdom
AU: Millard, P
EM: p.millard@macaulay.ac.uk
AF: Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, AB15 8QH United Kingdom
AU: Hunt, J
EM: HuntJ@landcare.cri.nz
AF: Landcare Research, PO Box 69, Lincoln, 8152 New Zealand
AU: Sommerkorn, M
EM: m.sommerkorn@macaulay.ac.uk
AF: Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, AB15 8QH United Kingdom
AU: Whitehead, D
EM: WhiteheadD@landcareresearch.co.nz
AF: Landcare Research, PO Box 69, Lincoln, 8152 New Zealand
AB: In the Rio Grande Plains of southern Texas, subtropical thorn woodlands have invaded areas that were once relatively open grasslands and savannas, resulting in increased ecosystem C and N storage and accelerated rates of C and N cycle processes. Climate change predictions for southern Texas indicate that rainfall and rainfall intensity may increase in this region. At present, we know little regarding short- or long-term responses of soil respiration to soil moisture variations, or how these variations may interact with grassland-to-woodland vegetation changes. The purpose of this study was to quantify short-term responses of soil respiration to a simulated 5 cm rainfall event in a subtropical savanna ecosystem. In each of 5 replicate woody patches, a transect was established from the center of the patch out into the surrounding grassland. Along each transect, 3 PVC collars (1 control, 2 irrigated) were installed at each of 4 sampling locations: (i) center of woody patch, (ii) halfway between center of woody patch and grassland, (iii) the woody patch/grassland edge, and (iv) out in the remnant grassland well-clear of woody influence. Irrigated collars received the equivalent of a 5 cm rainfall event at 0900 h, and soil respiration was measured at frequent intervals until approximately 1900 h of the same day using a LiCor-6400 IRGA. Soils from each transect location were then sampled to a depth of 30 cm and analyzed for bulk density, root biomass, C and N concentrations, and soil microbial biomass. Soil respiration in control plots ranged from 5 μmol CO₂ m^-2 sec^-1 in woody patches to 1 μmol CO₂ m^-2 sec^-1 in grasslands and showed little temporal variation. Within 30 min following the addition of 5 cm of water, soil respiration increased in all transect locations to 20-70 μmol CO₂ m^-2 sec^-1, and then declined exponentially over the next 8 h to approximately 10 μmol CO₂ m^-2 sec^-1 in woody patches and 5 μmol CO₂ m^-2 sec^-1 in grassland. The strong initial stimulation of CO₂ flux may have been due to physical displacement of soil gases by infiltrating water, accelerated root respiration, and/or slaking of rapidly wetted aggregates allowing microbial access to previously protected organic matter. Higher respiration rates in the woody patches are most likely attributable to greater root biomass and microbial biomass. Root biomass decreased linearly from the center of the woody patches (2560 g m^-2) to the grasslands (670 g m^-2). Soil microbial biomass also decreased from wooded patches (550 mg C kg^-1 soil) to grasslands (400 mg C kg^-1 soil) and was not affected by irrigation. Results of this study indicate that soil respiration was strongly influenced by the 5 cm simulated rainfall event, and the magnitude of this response was modulated by interaction with vegetation composition.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0476 Plant ecology (1851)
SC: Biogeosciences [B]
MN: Fall Meeting 2005